New standards and techniques of energy efficient building design have been developed in recent years in response to the increasing awareness of government, builders and consumers to the need for energy conservation. Fuel costs and resource-depletion concerns are two major driving factors toward energy efficient building design, and many regions have adopted stringent energy efficiency standards covering such areas as thermal insulation, water heating, space heating and ventilation and controlled air management.
Initial designs which promoted air-tightness of a building have been augmented by designs which focus on efficient usage of energy with a controlled exchange of stale indoor air and fresh outdoor air, in recognition of the potential health problems and structural damage which can result from a poorly ventilated environment. It is thus advantageous to integrate heating and ventilating functions, to achieve the most efficient usage of heating fuels while ensuring proper ventilation of the building for health and structural purposes.
An example of an integrated heater-ventilator is described and illustrated in U.S. Pat. No. 4,909,307 to Besik, which is incorporated herein by reference. The heater-ventilator has a heat exchange unit containing two regenerative heat exchange beds in isolated compartments. Air inlet to and exhaust from the compartments is controlled so that when one heat exchange bed is releasing sensible heat and moisture into the building air supply, the other heat exchange bed is recovering heat and moisture from the return air supply. The air flow through each heat exchange compartment is periodically reversed, so that the release and recovery functions alternate between the two heat exchange beds. This provides the advantage of preventing frost buildup in the heat exchange beds, which can significantly reduce sensible heat recovery efficiency, and allows the ventilator to be active whenever fresh air is required without being limited by the thermal state of the heat exchange bed. This configuration also facilitates moisture control, allowing for recovery of moisture in winter, during which the heat exchange beds retain moisture from the exhaust air stream and return it to the supply air stream when the air flow through the bed is reversed, and in summer effectively removing moisture from outdoor air before it is introduced into the dwelling, thus reducing the load on an air conditioning system.
The regenerative bed heat exchanger of U.S. Pat. No. 4,909,307 utilizes a pair of four-way shuttle valves comprising axially movable rods bearing dampers, housed in a valve compartment with a series of partitions, to control the alternate switching of recovery and release modes between the two heat exchange beds. This system presents certain disadvantages.
First, both valves must be actuated simultaneously in order to ensure that at all times at least one heat exchange bed is in the recovery mode and the other heat exchange bed is in the release mode. This requires adjoining valve rods creating a mechanical connection between the two valves, which complicates their construction and increases the size of the valve drive system.
Second, when the dampers are at intermediate points in the switching cycle they are remote from the inlet and outlet partitions, so there is a direct fluid communication between the stale air stream entering the heat exchange compartment and the fresh air stream being exhausted from the heat exchange compartment. This not only reduces the efficiency of the heat exchanger, it effectively restricts the stale air stream to clean air sources, such as the return air supply from the building, which will not release noxious fumes into the fresh air stream during switch-over intervals. This precludes the recovery of heat from other stale air sources such as bathroom and kitchen ventilators and combustion gas discharge, which can be a valuable sources of sensible heat.
Another disadvantage to this system is that the low energy blower in the heat exchange compartment cannot be active when the high energy furnace blower is inactive, as this would result in backflow from the heat exchange unit into the furnace. Thus, in order to ventilate the building during a period when the furnace is not active because there is no call for heat, both the heat exchange blower and the furnace blower must be activated. This results in unnecessary electrical energy consumption and, in most cases, unnecessarily high flow rates during any furnace-off/ventilator-on interval.
The present invention overcomes these disadvantages by providing valve means comprising a pair of valve members, in the preferred embodiment plastic discs, fixed on a common shaft to control the alternate switching of recovery and release modes between the two heat exchange beds. The valve members are mounted adjacent to inlet and outlet partitions containing the inlet and outlet ports, respectively, in communication with the heat exchange compartments. The valve members are provided with valve openings which, by rotating the shaft, are brought into alignment with the inlet and outlet ports to direct the fresh and stale air streams through the heat exchange beds. Because their rotational motion allows the valve members to remain in constant contact with the inlet and outlet partitions, even during switch-over cycles, there is no opportunity for leakage between the fresh and stale air streams. Moreover, since both valve members are mounted on a common shaft, construction of the valves is considerably simplified and a small servo motor can be used to drive the valve means.
The present invention also integrates the heating and ventilating functions by providing a damper upstream of the ventilator fresh air outlet to the furnace supply elbow, so that the low energy fresh air blower in the ventilator can be active when the high energy furnace blower is inactive without resulting in backflow from the ventilator into the furnace. The damper is biased by gravity to a closed position such that the force of air from the furnace air blower is sufficient to open the damper. The biasing force is controlled by an external counterweight which can be adjusted to ensure that the damper remains closed when the furnace blower is off, and that the furnace blower discharge will open the damper with minimal back pressure.
The present invention thus provides a regenerative bed heat exchanger, comprising an enclosed heat exchange compartment containing an air permeable regenerative heat exchange bed comprising a bed of a heat recovery medium capable of absorbing and releasing heat, for alternately absorbing heat from and releasing heat into an air stream, the bed having opposed air-permeable faces which permit a flow of air through the medium, an air inlet provided with a fresh air inlet port and a stale air inlet port, and an air outlet provided with a fresh air outlet port and a stale air outlet port, the heat exchange bed separating the fresh air inlet port from the stale air inlet port and separating the stale air outlet port from the fresh air outlet port such that a fresh air flow path is created through the fresh air inlet port, through the heat recovery medium and through the fresh air outlet port, and a stale air flow path is created through the stale air inlet port, through the heat recovery medium and through the stale air outlet port, and valve means for selectively simultaneously opening the stale air inlet port and the stale air outlet port while closing the fresh air inlet port and the fresh air outlet port, or simultaneously opening the fresh air inlet port and the fresh air outlet port while closing the stale air inlet port and the stale air outlet port.
The present invention further provides a ventilator comprising two regenerative bed heat exchangers each provided with a regenerative heat exchange bed, comprising a first enclosed heat exchange compartment containing a first air permeable heat exchange bed having a first air inlet provided with a first fresh air inlet port and a first stale air inlet port, and a first air outlet provided with a first air outlet port and a first stale air outlet port; a second enclosed heat exchange compartment containing a second air permeable heat exchange bed having a second air inlet provided with a second fresh air inlet port and a second stale air inlet port, and a second air outlet provided with a second air outlet port and a second stale air outlet port; the first and second heat exchange beds each comprising a bed of a heat recovery medium capable of absorbing and releasing heat, for alternately absorbing heat from and releasing heat into an air stream, each bed having opposed air-permeable faces which permit a flow of air through the medium, the first heat exchange bed separating the first fresh air inlet port from the first stale air inlet port and separating the first stale air outlet port from the first fresh air outlet port and the second heat exchange bed separating the second fresh air inlet port from the second stale air inlet port and separating the second stale air outlet port from the second fresh air outlet port such that a first fresh air flow path is created through the first fresh air inlet port, through the first heat exchange bed and through the first fresh air outlet port, a first stale air flow path is created through the first stale air inlet port, through the first heat exchange bed and through the first stale air outlet port, a second fresh air flow path is created through the second fresh air inlet port, through the second heat exchange bed and through the second fresh air outlet port, and a second stale air flow path is created through the second stale air inlet port, through the second heat exchange bed and through the second stale air outlet port; and valve means for alternately simultaneously opening the first stale air inlet port, the first stale air outlet port, the second fresh air inlet port and the second fresh air outlet port while closing the first fresh air inlet port, the first fresh air outlet port, the second stale air inlet port and the second stale air outlet port, or simultaneously opening the first fresh air inlet port, the first fresh air outlet port, the second stale air inlet port and the second stale air outlet port while closing the first stale air inlet port, the first stale air outlet port, the second fresh air inlet port and the second fresh air outlet port.
The present invention further provides a valve for a heat exchange apparatus comprising an enclosed heat exchange compartment containing an air permeable regenerative heat exchange bed comprising a bed of a heat recovery medium capable of absorbing and releasing heat, for alternately absorbing heat from and releasing heat into an air stream, the bed having opposed air-permeable faces which permit a flow of air through the medium, an air inlet provided with a fresh air inlet port and a stale air inlet port and an air outlet provided with a fresh air outlet port and a stale air outlet port, the heat exchange bed separating the fresh air inlet port from the stale air inlet port and separating the stale air outlet port from the fresh air outlet port such that a fresh air flow path is created through the fresh air inlet port, through the heat recovery medium and through the fresh air outlet port and a stale air flow path is created through the stale air inlet port, through the heat recovery medium and through the stale air outlet port, the valve comprising a rotating inlet valve member having a valve surface interposed between the air inlet partition and the heat exchange bed, comprising an inlet valve opening positioned to come into alignment with the stale air inlet port or the fresh air inlet port, and a rotating outlet valve member having a valve surface interposed between the air outlet and the heat exchange bed, fixed in position relative to the inlet valve member and comprising an outlet valve opening positioned offset circumferentially relative to the inlet valve opening, such that when the inlet valve opening comes into alignment with the stale air inlet port the outlet valve opening comes into alignment with the stale air outlet port, and when the inlet valve opening comes into alignment with the fresh air inlet port the outlet valve opening comes into alignment with the fresh air outlet port.
The present invention further provides an integrated forced air furnace and regenerative heat exchange apparatus, the furnace comprising a furnace blower for discharging a heated air stream into an air supply conduit and the heat exchange apparatus comprising a ventilation blower for discharging a fresh air stream into the air supply conduit, in which the air supply conduit is provided with a damper gravitationally biased to a closed position to prevent back-flow of the fresh air stream into the furnace when the ventilation blower is active and the furnace blower is inactive, wherein the biasing of the damper is capable of being overcome under a force of the furnace blower when the furnace blower is active.